1. Field of the Invention
The present invention relates generally to a brightness enhancement film, and more particularly, relates to the brightness used in a backlit liquid crystal display.
2. Description of the Related Art
A backlit liquid crystal display generally includes a brightness enhancement film which is typically positioned between a diffuser and a liquid crystal display panel. The backlit liquid crystal display also includes a light source such as a fluorescent lamp, a light guide for transporting light for reflection toward the liquid crystal display panel, and white reflector for reflecting light toward the liquid crystal display panel. The brightness enhancement film collimates light emitted from the light guide thereby increasing the brightness of the liquid crystal display panel. The increased brightness enables a sharper image to be produced by the liquid crystal display panel and allows the power of the light source to be reduced to produce a selected brightness. The brightness enhancement film in the backlit liquid crystal display is useful in equipment such as computers, personal TVs, video recorders, mobile communication devices, and automobile and avionics instrument displays.
As shown in FIG. 1, International Publication No. WO96/23649, public on Aug. 8, 1996, discloses prevention of groove tip deformation in brightness enhancement film. A brightness enhancement film includes a base 101 having a first surface on which prisms 102 are formed by molding and a second surface that is substantially flat or planar and opposite the first surface. After molding, the brightness enhancement film 100 is cured so that it forms the prisms 102. This is followed by heat treating the prisms 102. Heat treating is performed at a temperature that is at least equal to a normal glass transition temperature of resin. Heat treating raises the glass transition temperature of the resulting polymer above approximately 333 K such that groove tip impression is reduced. The prisms 102 consist of a first facet 103 and a second facet 104 which are substantially flat or planar. A side-by-side arrangement of regular prisms 102 is preferred for optical performance in one direction because the facets of the prisms 102 refract in a single direction and can concentrate the light from the diffuser. However, one major drawback of WO96/23649 is that the prisms do not refract in two dimensions.
The present invention intends to provide a brightness enhancement film with prisms consisting of a brightness unit preferred for optical performance in two dimensions in such a way as to mitigate the above problem.